The knowledge to predictably prevent and appropriately treat decompression sickness (DS) and related conditions (aeroembolism, barotrauma, aseptic bone necrosis and consumptive coagulopathy) is lacking due to an inadequate understanding of the relevant physical, physiological and pathological responses to decompression. The proposed investigations will look at the interaction of inert gas tensions, content and bubbles with blood and selected tissues as it affects VA/Q distribution, shunt, dead space, coagulation function and vascular endothelial integrity. Such investigations will combine Doppler ultrasonic bubble detection, inert gas content and inert gas tension measurements in tissues and flowing blood while simultaneously monitoring VA/Q, cardiac output, platelet kinetics, platelet function, fibrinogen kinetics, coagulation factors, fibrinolysis, fluid compartments and endothelial damage. This will more precisely indicate the etiology of decompression sickness, allow more effective prevention and treatment techniques, provide insight into other clinical conditions which manifest common signs and symptoms and furnish a means to test some theoretical concepts of safe decompression.